1. International Symposium on Molecular Spectroscopy RH: Cold /Ultra-Cold /Physics 6/19/14 6/19/14 Paul L. Raston, Tao Liang, and Gary E. Douberly Infrared Laser Stark Spectroscopy and Ab Initio Computations of the OH  CO Complex Department of Chemistry, University of Georgia Athens, Georgia, USA

2. Acknowledgments Post-Doc: Paul Raston Graduate Student: Tao Liang Support: ACS-Petroleum Research Fund U.S. National Science Foundation (CAREER) U.S. Department of Energy, Office of Science (BES-GPCP)

3. Motivation OH+CO  [HOCO]*  H+CO 2 Oxidative conversion of CO to CO 2 in combustion environments Poster child for non-Arrhenius behavior  + M HOCO (cis / trans)

5. Notable Previous Spectroscopy FIR-LMR (trans-HOCO) T. Sears Pure rotational spectroscopy (cis/trans-HOCO) Y. Endo Transient IR Absorption (trans-HOCO) C. B. Moore Matrix Isolation (trans/cis-HOCO) M. Jacox Anion Photoelectron spectroscopy (trans/cis-HOCO) R. Continetti Sub-Doppler IR absorption (trans-HOCO) D. Nesbitt

6. J. Phys. Chem. A 2013, 117, 13255-13264.

8. Overtone action spectroscopy of the linear OH  CO complex

9. 10000 He atoms can dissipate  6 eV (  140 kcal/mol) Cooling timescale < 1  s, pick-up timescale  10  s Spectroscopic study of the outcome of both reactive and non-reactive “cold” collisions between picked-up reactants pick-up cells T=0.4 K

10. X Droplet beam ∙OH + (CH 3 ) 2 CO + ∙CH 3 Rough Pump Gate Valve AirVacuum O-ring seal Water cooled copper electrodes Ta filament / Quartz tube Hydroxyl Radical Production via Flash Vacuum Pyrolysis of TBHP

11. E laser E Stark E laser E Stark or  M = 0  M = ±1 Droplet Beam cw-OPO (idler  3  m) OH CODetect laser- induced depletion of ionization cross- section in mass channel m/z=17

12. Agrees with predicted redshift from OH at CCSD(T)/aug-cc-pVTZ

13. OH  CO 2  3/2 5B5B

14. E laser E Stark  M = ±1 Droplet Beam cw-OPO (idler  3  m) Stark Spectroscopy

15. Spectroscopic Analysis Parity conserving Hund’s case (a) basis Couples  and  electronic states independent of J Constant contribution absorbed into electronic origin

16. Spectroscopic Analysis Parity conserving Hund’s case (a) basis

17. Spectroscopic Analysis Parity conserving Hund’s case (a) basis

18. Spectroscopic Analysis Parity conserving Hund’s case (a) basis

19. Perpendicular Polarization:  M =  1

20. Debye

22. Vibrationally Averaged Permanent Dipole Moment O OH-CO OH-OC Planar, R = 4.0 Å surface Red: Dipole moment Contours = 0.1 Debye Black: Binding Energy Contours = 50 cm -1 CCSD(T)/Def2-TZVPD Strategy: DMC on a 4D PES to get  gs

23. Summary Sequential addition of OH and CO to He droplets leads exclusively to the formation of the linear OH  CO entrance channel complex. OH  OC formation preclude perhaps by long-range electrostatic effects Stark Spectra are indicative of large-amplitude motion in entrance-channel well.

25.  Quantization axis Orientational Anisotropy {P 2 cos  }

26. Random Polarization:  M = 0,  1